This invention relates to a display device with high moving image quality by suppressing the coloring phenomenon generated in the edge area of an image when scrolled in the black insertion driving.
The display, from the viewpoint of the moving image in particular, can be roughly classified into an impulse-type display and a hold-type display. In the impulse-type display, the brightness response is reduced immediately after scanning like the persistence characteristic of the CRT, while the hold-type display, like the liquid crystal display, continues to hold the brightness based on the display data to the next scan.
The feature of the hold-type display is that a superior display quality free of a flicker can be obtained for a still image. For the moving image, however, the display quality is extremely reduced by the moving image blur in which the edge portion of a moving object blurs in appearance.
This moving image blur is caused by the retinal after-image on the part of the observer who interpolates the display image before and after the movement of the display image with the brightness held while moving the line of sight with the movement of an object. Regardless of how the response speed of display is improved, therefore, the moving image blur is known not to be completely eliminated. An effective method known to overcome this problem is described in “Moving Picture Quality Improvement for Hold-type AM-LCDs, Taiichiro Kurita, SID 01 DIGEST”, in which the display image is updated with a shorter frequency or a black screen is inserted thereby to cancel the retinal after-image provisionally in the same manner as in the impulse-type display.
A typical display displaying the moving image is a TV receiver, of which the scanning frequency is standardized at 60 Hz for interlaced scanning in the NTSC signal or 50 Hz for sequential scanning in the PAL signal. In the case where the frame frequency of the display image generated based on this frequency is 60 Hz or 50 Hz, the frequency is not sufficiently high and the moving image blurs.
As a means for improving this moving image blur, US 2004/0155847A (JP-A-2004-240317) discloses a drive method in which one video signal is driven by a double or higher frame frequency and the desired brightness is obtained by combining the brightness of a plurality of frames thereby to realize the effect of black insertion without reducing the brightness.